const  babel  = require('@babel/core');
let    code  = `let  fn = (a,b) => a + b`;
let  r = babel.transform(code,{
      presets:[
            '@babel/preset-env'
      ]
});
console.log(r.code);

//输出：
// "use strict";

// var fn = function fn(a, b) {
//   return a + b;
// };
